The most prevalent groups of bitter acids found as components of hops are the alpha-acids and beta-acids, also referred to as humulones and lupulones, respectively. Both contribute bitterness to beer, but the alpha-acids are much more intense in this regard than the beta-acids. Producers of hop extracts have recently used liquid carbon dioxide under supercritical conditions. A by-product of the operation is a product which contains approximately 61 weight percent beta-acids, the remainder consisting essentially of other hop resins.
Quite apart from their use in beer, hops and hop acids have also been recognized as microbial inhibitors. More specifically, hop acids and resins have been shown to be primarily active against some gram positive bacteria and Mycobacteria. Activity against gram negative bacteria is far less pronounced. It has been suggested that the reduced effect was due to induced permeability of the cell membrane in gram positive bacteria, but was inactivated by the serum phosphatides in gram negative bacteria. Arch. Mikrobiol. 94, pp. 159-171, 1973.
Other more recent references have been identified, such as U.S. Pat. No. 5,286,506 (1994) and Larson, Yu, Price, Haas and Johnson, International Journal of Food Microbiology, 1996, which report on the use of beta acids as extracted from hops for controlling Listeria. More specifically, 6 to 50 ppm of beta acids, as extracted from hops, was found in media to protect against Listeria monocytogenes contamination, while in foods, depending on the specific food, higher levels (100-300 ppm) were necessary.
Attention is also directed to the following references: Agricultural and Biological Chemistry, Vol. 49, No. 2, pp 399-404 (1985) which discloses that humulone, lupulone and related compounds were found to have antifungal activities; Dissertation Abstracts, Vol. 53-08B, 1991, pp. 3861, reports that compounds derived from hops possess antibacterial activity, and more specifically, the antibacterial activity against Lactobacillus brevis was found to be pH-dependent; Journal of the Institute of Brewing, 99 (5) 405-411 (1993) reports on the results of studies investigating the ability of hop acids to inhibit beer spoilage activity; Journal of the Institute of Brewing, 99 (1) 43-48 (1993) reports on the antibacterial activity of hop bitter resins derived from recovered hopped worts. More specifically, strains of thermophilic Bacillus spp were identified which failed to grow in certain sweet worts derived from mashes to which centrate (recovered hop wort) had been added; J. Food Prot. Vol 57, No. 1, pp 59-61 (1994) reports on the antimicrobial activity of hop resins against Streptococcus salivarius. The two hop resins used were iso-alpha acid and beta resin; Agric. Biol. Chem., Vol. 49, No. 2, pp. 399-403 (1985) discloses that humulone, lupulone and related compounds as having antifungal activities; Lebensm. Ind. Vol. 28, No. 7, pp. 311-315 (1981) reports that tests showed that hop extract and isomerized hop extract have similar anti-microbial properties like hops, but the antimicrobial effect of the hops in beer production was low. J. Appl. Bacteriol., Vol. 72, No. 4, pp. 327-324 (1992) considered the antibacterial effect of weak acids derived from the hop plant Humulus lupulus. The antibacterial activity of trans-isohumulone was about 20 times greater than that of humulone, 11 times greater than colupulone, and nine times greater than that of trans-humulinic acid when the degree of ionization was taken into account.
However not all gram positive bacteria are sensitive to hop resins as is well known to the Brewer and see J. Fernandez and Will Simpson in J. App Bacteriology, 75 315-319 (1993). Also G. Haas and B. Barsoumian in J. Food Protection 57, 59-61 (1994) worked with a strain of Bacillus subtilis which was resistant.
None of the art noted above deals with the control of botulism, which is well-known as an acute intoxication manifested by neuromuscular disturbances after ingesting food containing a toxin elaborated by Clostridium botulinum. The causative agent is actually one of several types of exotoxins elaborated by the sporulating, anaerobic bacillus Clostridium botulinum, which causes human poisoning. Botulinum toxins are highly poisonous proteins resistant to digestion by gastrointestinal enzymes. Clostridium difficile is one of the major causes of diarrheal disease particularly in elderly humans treated with antibiotics. Very few antibiotics are effective and treatment of this infection is difficult at best. Only vancomycin of the well known antibiotics seems to be useful in treatment. Helicobacter pylori is a common cause of gastric ulcers and chronic active gastritis in humans. Ulcer relapses are common in humans treated with antibiotics or bismith nitrate. Other intervention strategies have to be sought and a nutritional or dietetic approach would be highly desirable.